1. Field of the Invention
The present invention relates to a router device having a label switching function and a label switched path control method.
2. Description of the Background Art
Recently, the use of the so called Internet as a communication network using IP (Internet Protocol) has spread rapidly, and the traffic amount and the number of connected nodes are increasing rapidly. A communication network using IP such as Internet is called a best effort type communication network in which a router device makes its best effort to try to carry out the IP packet processing, but a transfer quality is not guaranteed so that IP packet loss may occur when traffics are concentrated at the router device. However, there are demands for the guarantee of the transfer quality such as a transfer delay or an IP packet loss rate even in the IP communication network, as in the case of requiring QoS (Quality of Service) or CoS (Class of Service), for example.
With this background, there is a need for a faster/higher performance router device which is a basic constituent element of an IP communication network, especially the Internet. As a technique for fulfilling such needs, the label switching technique has been developed and its standardization is in progress. A label switch router (LSR) based on the label switching technique can realize a high performance packet transfer by transferring layer-3 packets using not only the conventionally used layer-3 address information but also a fixed length label that is set in correspondence to the layer-3 address information.
As a label switching technique based scheme for realizing a faster packet transfer, MPLS (Multi-Protocol Label Switching) scheme has been proposed (see R. Callon, et al., xe2x80x9cA Framework for Multiprotocol Label Switchingxe2x80x9d, Internet Draft draft-ietf-mpls-framework-02.txt, November 1997, for example). In MPLS, a specific xe2x80x9clabelxe2x80x9d is assigned to packets belonging to a specific unit of management between label switch routers, an input side label and an output side label are stored in correspondence at each label switch router, and the label switching is carried out by referring to this information, so as to realize a fast packet transfer by omitting the IP processing. For example, in the case where the link layer is ATM, VPI/VCI (Virtual Path Identifier/Virtual Channel Identifier) is used as a label. A route through which packets are label switched will be referred to as a label switched path (LSP).
Here, at a time of generating the label switched path using the label switch router, the following two methods are available.
One method is a topology driven method in which one label switched path is generated for one entry of a routing table. In this method, the label switched paths are always set up for all the entries (all the destinations, for example) of the routing table regardless of the actual traffic state.
Another method is a traffic driven method in which a label switched path is generated when a specific packet arrives, with respect to its source address and destination address. In this method, the label switched path is set up only for a source address and destination address pair for which the packet transfer is actually carried out.
Now, when the application of these methods to the Internet is considered, in the case of using the topology driven method for allocating one label switched path to one entry of the routing table, the Internet backbone currently has approximately 50000 pieces of the routing information so that the required number of label switched paths becomes as much as approximately 50000. Also, in the case of using the traffic driven method for allocating a label switched path to a pair of the source address and the destination address for which the packet transfer is actually carried out, if the current Internet backbone is used, it is known that a considerable number (in a range of 5000 to 10000, for example) number of label switched paths are still required.
When the number of label switched paths is increased as such, many resources will be required for the label switched paths so that the implementation becomes difficult and costly.
Thus the conventional label switching requires to set up a considerable number of label switched paths when the network scale becomes large, so that it has been associated with serious problems regarding implementation and cost.
As a scheme for reducing the number of labels, a scheme called ARIS has been proposed (see A. Viswanathan, et al., xe2x80x9cARIS: Aggregate Route-Based IP Switchingxe2x80x9d, Internet Draft draft-viswanathan-aris-overview-00.txt, March 1997; and N. Feldman, et al., xe2x80x9cARIS Specificationxe2x80x9d, Internet Draft draft-feldman-aris-spec-00.txt, March 1997). This scheme uses a downstream initiated procedure in which the label allocation starts from an egress router.
However, in the case of using an upstream initiated procedure in which the label allocation starts from an ingress router as in the commonly assigned copending U.S. patent application Ser. No. 08/649,514, for example, there has been no known scheme for realizing the reduction of the number of labels.
Note that the reduction of the number of labels can contribute to the reduction of router resources. In particular, in the case of utilizing ATM, the number of labels is given by the number of ATM VCs but not so many ATM VCs can be handled in practice because of the limitations related to the implementation, so that it is important to reduce the number of labels.
It is therefore an object of the present invention to provide a router device and a label switched path control method capable of reducing the number of label switched paths to be set up and thereby making the device implementation easier.
It is another object of the present invention to provide a router device and a label switched path control method capable of reducing the number of labels by an upstream initiated procedure in which the label allocation starts from an ingress router.
According to one aspect of the present invention there is provided a router device, comprising: a first memory configured to store a router identification information of a target router to be set as an egress router if possible, at a time of setting up a label switched path from the router device as an ingress router; a control unit configured to carry out a control to set up the label switched path to the target router stored in the first memory; a second memory configured to store in correspondence a label switched path identification information of the label switched path set up according to the control by the control unit and an address information to be given to packets that are to be transferred by passing through the target router stored in the first memory; and a routing processing unit configured to carry out a routing processing for the packets according to the label switched path identification information and the address information stored in the second memory.
According to another aspect of the present invention there is provided a label switched path control method at a router device, comprising the steps of: (a) storing a router identification information of a target router to be set as an egress router if possible, in an egress router list, at a time of setting up a label switched path from the router device as an ingress router; (b) carrying out a control to set up the label switched path to the target router stored in the egress router list; (c) storing in correspondence a label switched path identification information of the label switched path set up according to the control by the control unit and an address information to be given to packets that are to be transferred by passing through the target router stored in the egress router list, in a routing table; and (d) carrying out a routing processing for the packets according to the label switched path identification information and the address information stored in the routing table.
According to another aspect of the present invention there is provided a computer usable medium having computer readable program code means embodied therein for causing a computer to function as a router device, the computer readable program code means includes: first computer readable program code means for causing said computer to store a router identification information of a target router to be set as an egress router if possible, at a time of setting up a label switched path from the router device as an ingress router; second computer readable program code means for causing said computer to carry out a control to set up the label switched path to the target router stored by the first computer readable program code means; third computer readable program code means for causing said computer to store in correspondence a label switched path identification information of the label switched path set up according to the control by the second computer readable program code means and an address information to be given to packets that are to be transferred by passing through the target router stored by the first computer readable program code means; and fourth computer readable program code means for causing said computer to carry out a routing processing for the packets according to the label switched path identification information and the address information stored by the third computer readable program code means.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.